Tree lungwort, also called Lungwort , (Lobaria pulmonaria), a lichen that, because of its physical resemblance to the lungs, was once used to treat tuberculosis, pneumonia, and other lung diseases. Its elongated, forked thallus (12 to 18 centimetres), loosely attached at one end, is dark green when wet and greenish brown and papery when dry. The forked lobes have square ends.